Power output of a naturally aspirated internal combustion engine may be significantly increased by the addition of a turbocharger. Turbochargers include a compressor for providing air or an air fuel charge at a greater than ambient pressure and density to the combustion chamber of the internal combustion engine. The turbocharger also includes a turbine, driven by exhaust gases from the turbocharged engine.
In most prior art turbocharger designs, the compressor and turbine rotors are fixed for rotation on a single shaft. The shaft is normally supported on bearing assemblies with the compressor rotor and turbine rotor attached on opposite ends of the shaft with the bearing support assemblies positioned therebetween. It is common practice to attach the compressor wheel to the shaft by the engagement of an internally threaded nut onto the threaded end of the shaft. The nut is tightened onto the threaded shaft to fix the compressor rotor to the turbine rotor.
In conventional turbocharger designs, attachment of the compressor to the compressor-turbine shaft by a nut engaged on the threaded end of the shaft has been followed almost universally without regard to the limitations presented by this arrangement. In part, this approach has been routinely followed by designers and manufacturers of turbochargers because it has been successful to the extent that it accomplishes its assigned function. However, where the confronting surfaces between the face of the nut and the compressor rotor are not precisely perpendicular to the longitudinal axis of the shaft, tightening of the nut to engage it against the compressor rotor results in bending of the shaft. This in turn introduces an imbalance in the compressor rotor.